FR3075339A1 - HEAT EXCHANGER WITH SURFACE TEXTURING ELEMENTS AND PLATES - Google Patents

Abstract

 The invention relates to a heat exchanger of the brazed plate and fin type comprising a plurality of plates arranged parallel to each other so as to define a series of passages for the flow of a first fluid to be put in heat exchange relationship with at least a second fluid, at least one intermediate element (22) being arranged in a passage (33) formed between a first and a second plate (6, 7) and comprising at least a first assembly portion (121) positioned against the first plate (6), said first assembly portion (121) comprising a first pair of opposite secondary surfaces (121a, 121b) one of which (121a) is oriented on the side of the first plate (6) and the other (121b) is oriented on the side of the second plate (7), at least one surface texturing (23) in the form of a porous structure or of reliefs formed on a surface of the intermediate element (22), several fins or j wave ambes (123) delimiting, within the passage (33), several channels (26) for the flow of the first fluid, at least one fin or wave leg (123) having said surface texturing (23) . According to the invention, said first assembly portion (121) has the surface texturing (23) on at least that (121a) of the secondary surfaces of the first pair oriented towards the side of the first plate (6), and the first plate (6) comprises a first pair of opposite primary surfaces (6a, 6b) and has the surface texturing (23) on at least that (6b) of the primary surfaces (6a, 6b) oriented towards the side of the intermediate element ( 22). Associated manufacturing process.

Description

The present invention relates to a heat exchanger of the plate and fin type comprising an intermediate element with surface texturing, as well as a process for manufacturing such an exchanger.

The present invention finds particular application in the field of gas separation by cryogenics, in particular air separation by cryogenics (known by the acronym "ASU" for air separation unit) used for the production of gaseous oxygen under pressure. In particular, the present invention can be applied to a heat exchanger which vaporizes a liquid flow, for example liquid oxygen, nitrogen and / or argon by heat exchange with circulating gas, by air or nitrogen, for example.

If the heat exchanger is in the tank of a distillation column, it can constitute a vaporizer operating as a thermosyphon for which the exchanger is immersed in a bath of liquid descending the column or a vaporizer operating as a vaporization with a supplied film directly by the liquid falling from the column and / or by a recirculation pump.

The present invention can also be applied to a heat exchanger which vaporizes at least one flow of liquid-gas mixture, in particular a flow of mixture with several constituents, for example a mixture of hydrocarbons, by heat exchange with at least another fluid, for example natural gas.

The technology commonly used for an exchanger is that of aluminum exchangers with plates and fins or brazed waves, which make it possible to obtain very compact devices offering a large exchange surface.

These exchangers include separating plates between which are inserted heat exchange structures, generally corrugated or wave structures, formed of a succession of fins or wave legs, thus constituting a stack of passages for the various fluids to be put in heat exchange relationship.

The performance of an exchanger is linked to the heat exchange coefficient of the heat exchange structures in contact with the fluids. The coefficient of heat exchange of a structure depends in particular on the nature of the material constituting it, the porosity of this material, its roughness and the flow regime of fluids.

It is possible to modify the heat exchange coefficient of an exchange structure by modifying the geometry or the physicochemical properties of its surface. This makes it possible to increase the effective exchange surface and / or to modify the interactions between the fluid and the surface, by changing properties of the surface considered as its wettability or its capacity to intensify the boiling of a fluid. We then speak of intensified surfaces.

For example, it is possible to make surface deposits of porous or textured coatings, forming reliefs on the surface of structures, or else to create such surface conditions by mechanical treatments or by chemical attack.

Document WO-A-2005/075920 discloses various techniques for depositing porous coatings or texturing on the surface of a wave for a heat exchanger.

One problem concerns the assembly of elements comprising intensified surfaces.

During the manufacture of a brazed aluminum exchanger, the constituent elements of the exchanger are linked together by brazing with the use of a filler metal, called brazing or brazing agent, the assembly being obtained by melting and diffusion of the brazing agent within the parts to be brazed, without fusion of these.

In general, in order to optimally guarantee the mechanical and / or thermal properties of the brazed joints, and thus to maximize the resistance of the exchanger to high fluid pressures, surface texturing on the portions of the structures is avoided. exchange at which a brazing joint must be formed.

However, this involves locally modifying the surface condition of these parts, which complicates the manufacturing process. For example, you can mask the areas where brazing should take place or remove the coating from these areas before brazing. However, these additional steps entail additional cost and implementation difficulties.

Another possibility is to texturize the heat exchange structures after brazing these structures in the exchanger.

However, it is then difficult to access the channels formed by the exchange structures in the exchanger passages and it is impossible to use mechanical texturing or thermal spray coating techniques. Other surface treatment techniques are difficult to implement. For example, for techniques involving preliminary stages of heat treatment or deposition of an impregnation layer to ensure adhesion of the coating, the entire exchanger must be treated. There is then a risk of blocking the channels, unbrapping parts of the exchanger or creating fragile metallurgical phases and damaging the brazed matrix.

Furthermore, it has been proposed to produce surface textures on the separating plates before brazing. Document WO-A-2004/109211 describes a method of depositing a porous coating on the surface of a separating plate of a heat exchanger. In this case, there is no brazed heat exchange structure between the plates. Exchange structures also have a role of spacers. They contribute to the rigidity of the exchanger passages and their resistance to compression during vacuum brazing of the exchanger. It may then be necessary to arrange additional reinforcement bars in the passages and to double the thickness of the plates.

The object of the present invention is to solve all or part of the problems mentioned above, in particular to facilitate the manufacture of a heat exchanger of the brazed plate and fin type having exchange structures with improved thermal properties.

The solution according to the invention is then a heat exchanger of the type with brazed plates and fins comprising a plurality of plates arranged parallel to each other so as to define a series of passages for the flow of a first fluid to be put in relation to heat exchange with at least a second fluid, at least one intermediate element being arranged in a passage formed between a first and a second plate and comprising:

- At least a first assembly portion positioned against the first plate, said first assembly portion comprising a first pair of opposite secondary surfaces of which one of the surfaces of the first pair of secondary surfaces is oriented towards the side of the first plate and the other of the surfaces of the first pair of secondary surfaces is oriented towards the side of the second plate,

- at least one surface texturing in the form of a porous structure or reliefs formed on a surface of the intermediate element,

- Several fins or wave legs delimiting, within the passage, several channels for the flow of the first fluid, at least one fin or wave leg having said surface texturing, characterized in that said first assembly portion has the surface texturing on at least that of the secondary surfaces of the first pair oriented on the side of the first plate, and the first plate comprises a first pair of opposite primary surfaces and has the surface texturing on at least that of the primary surfaces oriented on the side of the insert.

Depending on the case, the element of the invention may include one or more of the following technical characteristics:

- the first assembly portion has the surface texturing on the surface of the first pair oriented towards the side of the second plate.

the intermediate element has at least a second assembly portion positioned against the second plate, said second assembly portion comprising a second pair of opposite secondary surfaces, one of the secondary surfaces of the second pair being oriented on the side of the first plate and the other of the secondary surfaces of the second pair being oriented on the side of the second plate, the second assembly portion having the surface texturing on the surface of the second pair oriented on the side of the second plate.

- the second plate comprises a second pair of opposite primary surfaces, that of the primary surfaces oriented towards the side of the intermediate element having, at least in part, the surface texturing.

- at least one fin or wave leg comprises a third pair of opposite secondary surfaces, one and the other of said surfaces of the third pair having the surface texturing.

- the fins or wave legs follow one another in a lateral direction and extend in the passage generally in a longitudinal direction which is parallel to the first and second plates and orthogonal to the lateral direction.

the surface texturing is in the form of a porous structure having an open porosity of between 15 and 60%, preferably an open porosity of between 20 and 45%,% by volume, or in the form of reliefs defining, in cross section, open cavities on the surface of the first and second intermediate elements.

a brazing agent is arranged between the first plate and the intermediate element and / or between the second plate and the intermediate element.

the brazing agent is in the form of at least one coating layer arranged between the primary surface of the first plate oriented towards the side of the intermediate element and the surface texturing and / or between the primary surface of the second plate oriented towards the side of the intermediate element and the surface texturing.

the brazing agent has a thickness of less than 300 μm, preferably between 50 and 200 μm.

- The primary surfaces of the first and second plates oriented on the side of the intermediate element are free of brazing agent on their portions extending opposite said intermediate element.

the intermediate element is assembled in the passage by assembling at least said first assembly portion with the first plate, said assembly being produced by metallurgical bonding of the surface texturing present on that of the secondary surfaces of the first portion d 'assembly oriented on the side of the first plate with the surface texturing present on that of the primary surfaces of the first plate oriented on the side of the intermediate element, said surface texturing being bonded directly to each other or via a soldering agent.

the passage has an overall shape of parallelepiped delimited by two longitudinal edges and two lateral edges, at least one closing bar extending in the height of the passage, defined as the distance between the first plate and the second plate measured in a direction stacking perpendicular to the plates, along at least one of the longitudinal and lateral edges of the passage, the primary surfaces of the first and second plates oriented towards the side of the intermediate element being free of surface texturing on their portions extending next to the closing bar.

- a brazing agent is arranged on the portions of the primary surfaces of the first and second plates oriented towards the side of the intermediate element extending opposite the closing bar.

- the intermediate element has, before being assembled in the passage, a predetermined height, measured in a stacking direction perpendicular to the first and second plates, slightly greater than the height of the passage, defined as the difference between the first plate and the second plate measured in a stacking direction perpendicular to the plates.

According to another aspect, the invention relates to a method for manufacturing a heat exchanger of the brazed plate and fin type, said method comprising the following steps:

- arrangement of several plates parallel to each other so as to define a series of passages for the flow of a first fluid to be put in heat exchange relationship with at least one second fluid,

- arrangement of at least one intermediate element in a passage formed between a first and a second plate,

- Formation of at least one contact or quasi-contact zone between at least a first assembly portion of the intermediate element and the first plate, said first assembly portion comprising a first pair of opposite secondary surfaces, the one of the surfaces of the first pair is oriented on the side of the first plate and the first plate comprising a first pair of opposite primary surfaces, one of which is oriented on the side of the intermediate element, characterized in that said secondary surface and said primary surface have at least one surface texturing in the form of a porous structure or reliefs formed on surfaces of the first plate and of the intermediate element, the assembly of the first assembly portion with the first plate being carried out without a brazing agent, said method further comprising the following steps:

- application of a compressive force and supply of heat at least at the level of said contact or quasi-contact zone so as to form a metallurgical bond directly between said surface textures.

The present invention will now be better understood thanks to the description which follows, given solely by way of nonlimiting example and made with reference to the attached diagrams, among which:

Figure 1 illustrates an example of a heat exchanger comprising an intermediate element according to the invention;

Figure 2 illustrates an example of assembly of an intermediate element according to the invention assembled with a heat exchanger plate;

Figures 3 and 4 illustrate a three-dimensional view and a cross-sectional view of an intermediate element according to an embodiment of the invention;

Figures 5 and 6 illustrate different embodiments of an intermediate element assembled between two exchanger plates.

In a manner known per se, a heat exchanger comprises a stack of plates arranged parallel one above the other with spacing and thus forming several series of passages of parallelepiped shape and flat for the flow of a first fluid and at least one second fluid to be put into indirect heat exchange relationship via the plates. Preferably, the first fluid comprises a refrigerant to be vaporized at least partially.

Figure 1 schematically illustrates an example of passage 33 of an exchanger 1 of the vaporizer-condenser type supplied with liquid oxygen. This vaporizer-condenser vaporizes the liquid oxygen OL under low pressure (typically slightly higher than atmospheric pressure) collected at the bottom of a column, by condensation of medium pressure nitrogen (typically from 5 to 6 bars absolute) circulating in passages adjacent passages 33 (not shown) dedicated to the circulation of oxygen. Medium pressure nitrogen is most often taken in the gaseous state at the top of a medium pressure air distillation column to which the low pressure column mentioned above is connected. After its passage and at least partial condensation in the vaporizer-condenser, this nitrogen is returned to the medium pressure column.

It is more specifically in the context of this application that the invention will be described below, it being understood that its application can be envisaged in other contexts, in particular with fluids of another nature. Thus, the exchanger 1 can vaporize at least one flow of liquid-gas mixture, in particular a flow of mixture with several constituents, for example a mixture of hydrocarbons, by heat exchange with at least one other fluid, for example natural gas.

In particular, the invention may relate to a method of heat exchange between a first fluid and at least one second fluid in a heat exchanger according to the invention, said first fluid flowing in passage 33 at a lower pressure or equal to 5 bar, preferably a pressure between 1 and 2 bar.

All or part of the passages 33 of the exchanger 1 are provided with intermediate elements 22 defining, within the passages 33, channels 26 for the circulation of liquid oxygen and which can take different forms.

The intermediate elements 22 can have wavy shapes, as shown in Figures 3 and 4, and include wave legs 123 connected alternately by wave vertices 121 and wave bases 122. In this case, we call "Fins" the wave legs which connect the summits and the successive bases of the wave.

The intermediate elements 22 can take other particular forms defined according to the desired fluid flow characteristics. More generally, the term "fins" covers blades or other secondary heat exchange surfaces, which extend between the primary heat exchange surfaces, that is to say the plates of the exchanger, in the exchanger passages.

The intermediate elements 22 are generally linked by brazing to the separating plates of the exchanger. The connection can be made by vacuum brazing with the use of a filler metal 30, called brazing or brazing agent, the assembly being obtained by melting and diffusion of brazing agent 30 within the parts to be brazed, c that is to say in the base metal, without fusion of these.

Figure 2 is a partial view of an intermediate element 22 assembled to a first plate 6 adapted to define, in association with another directly adjacent second second plate 7 (not shown), a passage 33 of the exchanger 1.

The intermediate element 22 and the plate 6 respectively comprise assembly portions 121.60 intended to be assembled with each other. The assembly portions 121, 60 are positioned one against the other, preferably with a slight clearance between them in order to interpose therein the brazing agent 30. Typically the assembly portions 121, 60 may be those where the clearance between the pieces 22, 6 is the lowest, typically the portions at which the pieces 22, 6 are in contact with each other or in quasi-contact, that is to say with a very clear weak existing between all or part of said portions, with each other.

As seen in cross section in Figure 4, the intermediate element 22 comprises a plurality of fins or wave legs 123 configured to delimit, when the element 22 is mounted between the first plate 6 and the second plate 7, a plurality first fluid flow channels 26.

The element 22 further comprises at least a first assembly portion 121 configured to be assembled with the first plate 6 and comprising a first pair of opposite secondary surfaces 121a, 121b, one 121a of the secondary surfaces of the first pair being oriented on the side of the first plate 6 and the other 121b of the secondary surfaces of the first pair being oriented on the side of the second plate 7 when the intermediate element 22 is in the assembled state.

The intermediate element 22 further comprises at least one surface texturing 23 in the form of a porous structure or of reliefs formed on a surface of the intermediate element 22.

In the context of the invention, at least one surface texturing 23 is present on a surface of at least one fin or wave leg 123 of the intermediate element 22. It should be noted that the intermediate element may have one or more predetermined forms of surface texturing distributed over different zones of its surface, it being understood that a surface texturing can as well be carried out in the surface of the material constituting the intermediate element as it is deposited therein; ie result from an addition of additional material on the surface of the intermediate element.

According to the invention, said first assembly portion 121 has the surface texturing 23 on at least that 121a of the secondary surfaces of the first pair oriented towards the side of the first plate 6.

In addition, the first plate 6 comprises a first pair of opposite primary surfaces 6a, 6b and has the surface texturing 23 on at least that 6b of the primary surfaces 6a, 6b oriented towards the side of the intermediate element.

22.

The inventors of the present invention have demonstrated that for certain applications, the assembly of interleaved elements with surface texturing could be carried out without special preparation of the assembly portions and lead to satisfactory performance in terms of mechanical strength. This is particularly the case when in operation, the channels 26 defined between the parts 22, 6 channel a first fluid whose pressure is relatively low, typically less than or equal to 5 bar, preferably a pressure between 1 and 2 bar , as is the case in the passages for oxygen of the vaporizer-condenser previously described.

In addition, it was found that the surface texturing could participate in a beneficial way in the formation of a brazed joint. Indeed, the solder being trapped in the porosity or the cavities of the coating by capillary forces, it has less tendency to diffuse through the intermediate element, which limits the risks of dissolution of the material constituting this element and allows reduce the thickness. The filling of pores or cavities also leads to better heat transfer performance between the brazed parts, as well as to better mechanical strength of the assembly.

Thanks to the invention, the manufacturing process is simplified since the surface texturing 23 can be formed or deposited on the surface of the plate and of the intermediate element without requiring any additional masking or post-processing step aimed at eliminate the surface texturing of the portions to be assembled. Texturing is formed on the parts before assembly, which preserves the integrity of the exchanger matrix.

Preferably, the first assembly portion 121 has the surface texturing 23 on the secondary surface 121b of the first pair oriented towards the side of the second plate 7.

In addition, the fins or wave legs 123 include a third pair of opposite secondary surfaces 123a, 123b. Preferably, the first assembly portion 121 of the first intermediate element 221 is arranged between two successive fins or wave legs 123, the surface 121b oriented towards the side of the second plate 7 having two ends each connected to a secondary surface 123a of each of the two fins or wave legs 123.

Preferably, one and the other of the surfaces 123a, 123b of the third pair having the surface texturing 23.

Thus, two successive fins or wave legs 123 delimit between them a channel 26, the wall formed by the first assembly portion, and the side walls, formed by the two fins 123, have internal surfaces with an exchange coefficient. improved thermal.

According to a particular embodiment, the intermediate element 22 has at least a second assembly portion 122 configured to be assembled with the second plate 7, said second assembly portion 122 comprising a second pair of opposite secondary surfaces 122a, 122b , one 122a of the secondary surfaces of the second pair being oriented towards the side of the first plate 6 and the other 122b of the secondary surfaces of the second pair being oriented towards the side of the second plate

7.

It is thus possible to assemble another portion of the intermediate element 22 to a reciprocal assembly portion on the first plate 7 during the manufacture of the exchanger, which further improves the solidity and the rigidity of the passage 33.

Preferably, the second assembly portion 122 has the surface texturing 23 on its two secondary surfaces 122a, 122b of the second pair oriented towards the side of the second plate 7.

As in the example in FIG. 4, the second assembly portion 122 of the intermediate element 22 can be arranged between two fins or wave legs 123, the surface 122a of the second pair oriented towards the side of the first plate 6 having two ends each connected to a secondary surface 123b of each of the two fins or wave legs 123, said surface 122a of the second pair and said secondary surfaces 123b having the surface texturing 23.

Thus, the manufacturing process of the intermediate element is simplified since the surface texturing can be formed or deposited on all or almost all of the surfaces of the intermediate element without requiring any additional masking or post- treatment aimed at eliminating the surface texturing of the portions to be assembled.

According to a particular embodiment, the surface texturing 23 is formed on all or almost all of the intermediate element 22.

Note that in the context of the present invention, almost all of a surface or of an element means a portion representing at least 90%, preferably at least 95%, more preferably at least 98 % of the area of this area or the total area of this element.

According to a particular embodiment, the intermediate element 22 is a corrugated product comprising a succession of wave legs 123 connected alternately by wave vertices 121 and wave bases 122. At least one wave vertex 121 comprises a first assembly portion 121 according to the invention.

The following explanations are made with reference to Figures 4 to 6, it being understood that the intermediate element 22 can take any other suitable form and does not necessarily include all the characteristics detailed below.

Figure 4 shows a cross-sectional view of a corrugated heat exchange structure 22. Several wavelengths 123 of elongate shape extend parallel to each other and generally in a direction known as longitudinal z. The wave legs follow one another in a lateral direction x, which is perpendicular to the longitudinal direction z, and are connected alternately by wave vertices 121 and wave bases 122.

According to the example illustrated in FIG. 4, the wave vertices 121 and wave bases 122 are of planar shape and extend parallel to each other and perpendicular to the wave legs 123. The channels 26 for the first fluid , which are formed between two successive wave legs and an apex or base arranged between said successive wave legs, thus have a generally rectangular cross section.

Figure 4 illustrates a straight wave with wave legs 123 with a flat surface. Other intermediate element configurations 22 are of course conceivable, in particular configurations of the perforated straight wave, partial offset wave, wave wave or herringbone type ("herringbone" in English).

An element 22 according to Figure 4 is visible in Figures 5 or 6 in the mounted state, that is to say mounted between a first and a second plate 6, 7 directly adjacent forming a passage 33. The passage 33 is of generally parallelepiped shape and configured to channel the first fluid parallel to the longitudinal direction z.

In operation, the first fluid flows over the width of the passage 33, measured in the lateral direction x, between an inlet and an outlet of the passage 33 located at two opposite ends along the length of the passage 33, measured in the longitudinal direction z . The wave legs 123 delimit within the passage 33 a plurality of channels 26 which extend parallel to the longitudinal direction z.

As seen in Figures 5 or 6, the element 22 preferably extends over almost all, if not all, of the height of the passages, measured in a vertical direction y perpendicular to the plates 6, 7, so as to be in contact or almost in contact with the plates 6, 7. The wave vertices 121 and the wave bases 122 are arranged parallel to the plates 6,

7.

Preferably, the intermediate element 22 is arranged in a so-called “easyway” configuration in the passage 33, that is to say that the wave legs 123 extend generally in the direction of flow of the first fluid in the passage 33. Note that in service, the direction of flow of the first fluid is preferably vertical, the direction of flow can be ascending or descending.

Advantageously, an intermediate element 22 according to the invention may be arranged in a zone 3 of a passage 33 of the exchanger into which the rising oxygen penetrates, the intermediate element thus having porosities or reliefs multiplying the sites on the surface. priming for the formation of oxygen gas bubbles OG.

Preferably, each wave summit 121 comprises a first assembly portion 121 according to the invention. The surface 121a of the wave summit positioned against the first plate 6 thus has at least one surface texturing 23.

Note that the terms "positioned against" mean a portion of assembly juxtaposed to a plate, with or without play existing between all or part of the portion and the plate.

Advantageously, each wave base 122 comprises a second assembly portion 122 configured to be assembled, in the assembled state, with the second plate 7.

As illustrated in FIG. 4, said second assembly portion comprises a second pair of opposite surfaces 122a, 122b, that 122b of the surfaces of the second pair oriented towards the side of the second plate 7 having at least one surface texturing 23.

Preferably, each wave leg 123 comprises a third pair of opposite surfaces 123a, 123b, each of the surfaces 123a, 123b of the third having said surface texturing 23, preferably over all or almost -totalité.

Preferably, said first assembly portions 121, the fins or wave legs 123, and said second assembly portions 122 if present, are in one piece, i. e. made in one piece.

FIG. 5 illustrates an example where all the wave legs 123 have at least one surface texturing on their two surfaces 123a, 123b. Each channel 26 thus has two side walls whose internal surfaces are intensified.

Preferably, the first assembly portion 121 also has the surface texturing 23 on the surface 121b of the first pair positioned, in the assembled state, against the second plate 7. The second assembly portion 122 may also have the surface texturing 23 on the surface 122a of the second oriented pair, in the assembled state, on the side of the first plate 6. This makes it possible to maximize the surface texturing surface 23 present on the intermediate element 22 and therefore to maximize the efficiency of thermal transfer within the channels 26 delimited by the intermediate element.

Such a configuration is illustrated in FIGS. 5 and 6. In fact, each channel 26 has an internal surface formed, in the assembled state, alternately by the surface 122a of a wave base 122 oriented towards the first plate 6, the surface 6b of the first plate 6 oriented towards the wave base 122 and the respective surfaces 123a, 123b of the two wave legs 123 connected to the ends of said wave base 122, and by the surface 121b of a vertex wave 121 oriented towards the second plate 7, the surface 7a of the second plate 7 oriented towards the wave summit 121 and the respective surfaces 123a, 123b of the two wave legs 123 connected to the ends of said wave summit 121 .

By arranging at least one surface texturing 23 on the surfaces of the intermediate element 22 as well as on the surfaces of the plates 6, 7, the heat exchange within the channels 26 is intensified.

Preferably, the corrugated product 22 has the surface texturing 23 on all or almost all of its surfaces.

Advantageously, the corrugated product 22 can be formed from a flat product, such as a sheet or strip, having two opposite surfaces 22a, 22b. Both of these surfaces 22a, 22b have the surface texturing

23. This product is then shaped mechanically, for example by a press tool, then arranged in a passage of the exchanger.

Advantageously, at least one surface texturing 23 is formed on one and the other of said opposite faces 22a, 22b. Preferably, the opposite faces 22a, 22b on which the surface texturing 23 is formed have said texturing, over all or almost all of it. The face 22a gives rise, after shaping, to the surfaces 121a, 123b, 122a of the corrugated product of Figure 4. The face 22b gives rise, after shaping, to the surfaces 123a, 121b, 122b of the corrugated product of Figure 4.

Note that almost all of a face means a portion representing at least 90%, preferably at least 95%, more preferably at least 98% of the area of this face.

According to this embodiment, all the surfaces of the product 22 located, in the assembled state, on the side of the second plate 7 and all the surfaces of the product 22 located, in the assembled state, on the side of the first plate 6, therefore have a surface texturing 23.

In the context of the invention, the corrugated product 22 is preferably formed from a flat product, such as a sheet or sheet, having a thickness of at least 0.15 mm, preferably between 0.2 and 0.4 mm. This thickness is indicated by the letter "t" in Figure 3. The implementation of a surface texturing 23 requires significant heat fluxes, in particular when the function of the surface texturing 23 is to intensify the boiling of the first fluid. It is therefore advantageous to use a relatively thick intermediate element, in order to maintain the highest possible coefficient of fins, that is to say a better ability of the fins to transmit heat.

It is also advantageous to work with a thicker intermediate element when, due to the intensification of the heat exchanges obtained thanks to the surface texturing, it is desired to reduce the density of fins of the intermediate element in order to reduce the losses of charges it generates. The coefficient of heat exchange of the intermediate element is then preserved by increasing its thickness.

It being noted that the fin coefficient is a number typically between 0 and 1, this being equal to 1 at the point of contact with an adjacent plate and decreasing on the fin when moving away from the plate. The point in the middle of the fin is the point with the lowest fin coefficient. Working with thicker fins reduces heat conduction through the fin from the plate to the mid point of the fin, which increases the coefficient of the fin.

Preferably, the corrugated product 22 has a density, defined as the number of wave legs per unit of length measured along the lateral direction x, less than 18 legs by 2.54 centimeters, preferably less than 10 legs d wave per 2.54 cm, more preferably less than or equal to 5 legs per 2.54 cm. Advantageously, the density can be between 1 and 5 legs by 2.54 centimeters. Note that these density values are applicable to an intermediate element which is not necessarily a corrugated product, the fins following each other in the lateral direction x and the density then being defined as the number of fins per unit of length, measured in the lateral direction x.

The use of a relatively low density makes it possible to facilitate the deposition phase of the surface texturing on the fins or struts, their surface being more accessible. In addition, the use of a lower density interlayer facilitates the removal of bubbles created at the surface texturing.

Preferably, the intermediate element 22 comprises a solid substrate, in particular a non-porous substrate, on which the texturing 23 is formed. Depending on the structure of the intermediate element, the substrate may comprise one or more first and / or second assembly portions, the fins or struts. Preferably, the surface texturing 23 covers all or almost all of the substrate.

Note that the intermediate element is preferably monobloc, that is to say formed in one piece.

In the context of the invention, the surface texturing 23 may result from a surface coating deposited on the element or else from a modification of the surface state of said part element obtained by chemical, mechanical or equivalent treatment , for example by sandblasting, grooving ....

In particular, the surface texturing 23 may result from a surface coating deposited on the substrates of the intermediate elements, in particular a coating deposited by the liquid route, in particular by soaking, spraying or by electrolytic route, by the dry route, in particular by deposition chemical vapor phase (in English Chemical Vapor Deposition or CVD) or physical vapor phase deposition (in English Physical Vapor Deposition or CVD), or by thermal spraying, in particular by flame or plasma.

Preferably, the surface texturing is formed from aluminum or an aluminum alloy comprising, for 100% of its mass, at least 80% by mass of aluminum, preferably at least 90%, more preferably at minus 99% aluminum.

According to a preferred embodiment, the surface texturing 23 is in the form of a porous structure, preferably a porous layer. The porous structure can for example be formed of a deposit of lightly sintered aluminum particles, of tangled aluminum filaments, of semi-molten aluminum particles stuck together, such as the aluminum particles which are obtained after projection which is obtained in flame thermal projection.

Preferably, the surface texturing 23 has, before assembly of the intermediate element, an open porosity of between 15 and 60%, preferably between 20 and 45%, more preferably an initial open porosity of between 25 and 35% ( % in volume). Note that the open porosity is defined as the ratio between the volume of the open pores, that is to say the pores communicating fluidically with the external environment in which the intermediate element is located, and the total volume of the porous structure .

The pores of the porous structure 23 preferably have a diameter between 1 and 200 μm, preferably between 5 and 100 μm. Being noted that the pores are not necessarily of circular section but can present irregular shapes. The term “diameter” therefore also covers an equivalent hydraulic diameter which can be calculated from measurement of the pressure drop undergone by a gas flow through the porous structure and assuming that the pores have a regular shape, in particular spherical, cylindrical, ...

We can also characterize the size of the pores by their volume. Preferably, the pores of the porous structure 23 have a volume of between 1000 and 1,000,000 μm ³ . The pore volume can for example be determined by tomography or by analysis of images of polished sections of samples taken in a multitude of directions in space.

Alternatively, the surface texturing 23 can be in the form of reliefs, or patterns, printed or produced in or on the material constituting the substrate of an intermediate element. Preferably, these reliefs define, in cross section, open cavities on the surface of the element. For example, various micro-reliefs or sizes or morphologies, such as discrete or uninterrupted grooves, streaks, protuberances, ... may be formed or deposited on the surface of the element considered. In particular, the reliefs forming the surface texturing 23 can be produced by laser or mechanical and / or chemical machining.

According to an embodiment illustrated in Figure 6, the intermediate element 22 can be assembled at least to the first plate 6, preferably to the first and second plates 6, 7 by brazing.

According to this embodiment, the assembly of the intermediate element 22 with the plates 6, 7 is obtained by melting and diffusion of the brazing agent 30 within the textures, and optionally of the base metal, of the element interlayer and plates. The textures of the intermediate element and of the plates are thus metallurgically linked by means of the soldering agent 30.

Preferably, the brazing between the first and second assembly portions 121, 122 of the intermediate element and the plates 6, 7 is carried out as part of the overall brazing of the matrix of the exchanger. The stack of plates, the intermediate elements and the other constituent elements of the exchanger are pressed against each other by means of a compression device. The matrix thus formed is placed in a vacuum oven and heated to temperatures between 550 and 650 ° C, preferably of the order of 580 to 600 ° C. The compression force applied to the matrix is generally of the order of 20,000 to 40,000 N / m ² .

Preferably, the plates 6, 7 of the exchanger are laminated plates comprising a central sheet 40, each face of which is coated with a layer of brazing agent 30. An example of such a plate 6 is illustrated in FIG. 2 According to another embodiment, the soldering agent 30 can take the form of a strip or a surface coating layer 30. The coating layer 30 can be deposited by spraying or by brush application of the brazing agent 30 in the form of a powder suspension containing the powder, a dispersant, a binder, additives for controlling the viscosity.

The soldering agent 30 is preferably formed from a metallic material having a melting temperature lower than that of the materials constituting the parts 6, 22. The parts 6, 22 and 30 are preferably formed from aluminum alloy. The plates 6 and the elements 22 of the exchanger are advantageously formed from a first aluminum alloy of the 3XXX family, preferably of the type 3003 (standard ASME SB-2019 SECTION 2-B). The soldering agent 30 is formed from a second aluminum alloy, preferably an alloy of the 4XXX type (ASME SB-2019 SECTION 2-B standard), in particular of the 4004 type.

As seen in Figures 5 and 6, the first and second plates 6, 7 respectively comprise a first and a second pair of opposite primary surfaces 6a, 6b, 7a, 7b. Preferably, the first and second plates 6, 7 have, at least on the portions of their primary surfaces 6b, 7a extending opposite the element 22, the surface texturing

23.

Preferably, each of the first and second plates 6, 7 forms with another adjacent plate another passage of fluid (not shown). Other intermediate elements 22 are also arranged in these other passages in accordance with the invention. Preferably, the primary surfaces 6a, 7b of the first and second plates oriented towards the side of these other elements and extending opposite said other elements also have at least one surface texturing.

Preferably, the first and second plates 6, 7 respectively have a brazing agent 30 in the form of a coating layer arranged between the primary surface 6b of the first plate 6 oriented towards the side of the intermediate element 22 and the texturing surface formed on said primary surface 6b, a brazing agent 30 in the form of a coating layer arranged on the primary surface 7a of the second plate 7 oriented towards the side of the intermediate element 22 and the surface texturing 23 on said primary surface 7a.

Advantageously, the soldering agent 30 has a thickness of less than 300 μm, preferably between 50 and 200 μm. Thus, an excess of brazing is avoided which would be detrimental to the performance of the exchanger since by flowing outside the zone of the brazed joint, the brazing could modify the microstructure of the coating or the surface texturing and therefore its performance. , by filling the porosities or cavities or by promoting the closing of the open porosity of the element with intensified surface.

According to a particular embodiment, the height of the element 22 can be adapted to the height of the passage 33 so that there is a clearance of a predetermined value, as indicated by the reference “d” in the Figure 6, between the wave vertices 121 and the first plate 6 and between the wave bases 122 and the second plate 7. This makes it possible to prevent capillary rise of the brazing agent outside the zone of the brazed joint during the vacuum brazing step, which can be detrimental to the performance of the exchanger since by flowing, the brazing can modify the microstructure of the surface texturing by filling in the porosities or cavities present on the surface. Preferably, the clearance d is between 0 and 0.1 mm, preferably between 0 and 0.05 mm.

According to an alternative embodiment illustrated in Figure 5, the intermediate element 22 can be assembled at least to the first plate 6, not by brazing, but by metallurgical bond obtained directly between the surface texturing 23 present on that 121a of the surfaces secondary of the first assembly portion 121 oriented on the side of the first plate 6 and the surface texturing 23 present on that 6b of the primary surfaces of the first plate 6 oriented on the side of the intermediate element 22.

Thus, the inventors of the present invention have demonstrated that by bringing the surface texturing portions of the intermediate element and the adjacent plate into contact, these could bond together due to their high heating. temperature combined with the effect of the compression force exerted during vacuum brazing of the entire exchanger.

This reduces or even avoids the risk of modifying the characteristics of the surface texturing outside the assembly portions. This method of assembly is particularly advantageous when the passages 33 are not put under overpressure, or else at a low pressure, that is to say less than or equal to 5 bar, during the operation of the exchanger, the requirements in terms of mechanical strength of the exchanger then being less important.

In particular, the direct metallurgical bond can be achieved by a method of sintering textures leading to their densification by diffusion of material. According to an alternative or complementary variant, the direct metallurgical bond can be produced by a metal interdiffusion process, also called diffusion welding, which leads to the bonding of the textures to each other by mutual diffusion of material.

The same type of bond can be produced between the surface texturing 23 present on that 122b of the secondary surfaces of the second assembly portion 122 oriented towards the side of the second plate 7 and the surface texturing 23 present on that 7a of the primary surfaces of the second plate 7 oriented towards the side of the intermediate element 22.

According to this method of assembly, the primary surfaces 6b, 7a of the first and second plates 6, 7 oriented towards the side of the intermediate element 22 are free of soldering agent 30 on their portions extending opposite said intermediate element 22 .

Preferably, the direct metallurgical connection between the first and second assembly portions 121, 122 of the intermediate element and the plates 6, 7 is carried out as part of the overall brazing of the matrix of the exchanger. The stack of plates, the intermediate elements and the other constituent elements of the exchanger are pressed against each other by means of a compression device. Contact zones are thus formed between at least a first plate and one or more first assembly portions of the intermediate elements and / or between at least a second plate and one or more second assembly portions of the intermediate elements. The matrix thus formed is placed in a vacuum oven and heated to temperatures between 550 and 650 ° C, preferably between 580 and 600 ° C. The compression force applied to the matrix is preferably between 20,000 and 40,000 N / m ² The matrix is subjected to a thermal brazing cycle with a total duration of between 10 and 30 hours.

For example, a thermal cycle with which one can metallurgically bond textures of surfaces directly between them consists of a first temperature ramp corresponding to a gradual rise in temperature up to the solidus temperature of alloy 4004, that is to say 565 ° C, in 4:43 min, maintaining at a temperature above 565 ° C for 3:30 min and a second temperature ramp corresponding to a gradual change in temperature from 565 ° C to 585 ° C for a period of 2:30 min.

Generally, the passage 33 has the shape of a parallelepiped delimited by two longitudinal edges and two lateral edges. Closing bars are arranged between the first and the second plate and extend along each edge of the passage so as to close it over its entire height and to ensure its sealing. The mechanical strength of the stack of plates is ensured by brazing the plates with the closing bars.

According to a particular embodiment, the intermediate element 22 has, before being assembled in the passage 33, a predetermined height h, measured in a stacking direction y perpendicular to the plates 6, 7, slightly greater than the height H of the passage 33. Preferably, the height h of the intermediate element 22 is greater than that H of the passage 33 by a multiplying factor of between 1.01 and 1.07. Thus, there is a crushing of the surface textures which promotes their nesting in each other at their contacting zone, so that there are more or almost no more pores or open cavities in this area. The thermal conductivity between the plate and the element 22 is thereby improved.

Figures 5 and 6 show a closing bar 16 which extends in the height H of the passage 33 along a longitudinal edge.

Preferably, the primary surfaces 6b, 7a of the first and second plates 6, 7 oriented towards the side of the intermediate element 22 are free of surface texturing 23 on their portions extending opposite the closure bar 16. An agent brazing 30 is arranged between said portions and the closing bar 16. Thus, the closing bar can be brazed more securely to the plates 6, 7, which provides greater mechanical resistance to the exchanger.

Preferably, after direct connection or by brazing of the first assembly portion with the first plate 6, the surface texturing 23 is modified at the level of said first assembly portion 121 and of the respective portion 60 of the positioned plate 6. against the first assembly portion 121. In particular, in the case of an assembly by brazing, at least part of the surface texturing 23 is infiltrated by the brazing agent 30 at the level of the assembly portions 220, 60 This effect is linked to the compressive force applied to the brazed parts and to the flow of the soldering agent 30 in the texturing.

Depending on the case, the open porosity or the cavities of the surface texturing 23 can be wholly or partially filled by the soldering agent 30 or by mutual interweaving of texturing at the first assembly portion 121 and the portion respective 60 of plate 6.

Preferably, after formation of the direct bond or by brazing, the surface texturing 23 has, at the first assembly portion 121 and the respective portion 60 of the plate 6, a residual open porosity of between 0% and 90 %, preferably between 10% and 50%, of the initial open porosity, that is to say before formation of the bond (0% indicating that the initial open porosity is completely filled following soldering or direct bonding) .

More generally, the surface texturing 23 can have, before bonding, at the level of the assembly portions 220, 60, an initial volume of open pores or cavities. After bonding, the surface texturing 23, at the level of the first assembly portion 121 and of the respective portion 60 of the plate

6, a residual volume of open pores or cavities representing from 0% to 90%, preferably from 10% to 50%, of the initial volume of open pores or cavities.

Advantageously, after bonding, the surface texturing 23 is kept outside the first assembly portion 121 and the respective portion 60 of the plate 6. In particular, the surface texturing 23 has, outside the portions assembly 121.60, an open porosity identical or almost identical to the initial open porosity and / or a volume of open pores or cavities identical or almost identical to the initial volume of pores or open cavities.

Claims (16)

1. Heat exchanger of the type with brazed plates and fins comprising a plurality of plates arranged parallel to each other so as to define a series of passages for the flow of a first fluid to be put in heat exchange relationship with at least one second fluid, at least one intermediate element (22) being arranged in a passage (33) formed between a first and a second plate (6, 7) and comprising: - At least a first assembly portion (121) positioned against the first plate (6), said first assembly portion (121) comprising a first pair of opposite secondary surfaces (121a, 121b), one of which (121a) is oriented on the side of the first plate (6) and the other (121b) is oriented on the side of the second plate (7), - at least one surface texturing (23) in the form of a porous structure or reliefs formed on a surface of the intermediate element (22), - Several fins or wave legs (123) delimiting, within the passage (33), several channels (26) for the flow of the first fluid, at least one fin or wave leg (123) having said texturing of surface (23), characterized in that said first assembly portion (121) has the surface texturing (23) on at least that (121a) of the secondary surfaces of the first pair oriented towards the side of the first plate (6) , and the first plate (6) comprises a first pair of opposite primary surfaces (6a, 6b) and has the surface texturing (23) on at least that (6b) of the primary surfaces (6a, 6b) oriented on the side of the 'intermediate element (22). 2. Exchanger according to claim 1, characterized in that the first assembly portion (121) has the surface texturing (23) on the surface (121b) of the first pair oriented towards the side of the second plate (7). 3. Exchanger according to one of claims 1 or 2, characterized in that the intermediate element (22) has at least a second assembly portion (122) positioned against the second plate (7), said second portion of assembly (122) comprising a second pair of opposite secondary surfaces (122a, 122b), one (122a) of the secondary surfaces of the second pair being oriented towards the side of the first plate (6) and the other (122b) of the secondary surfaces of the second pair being oriented on the side of the second plate (7), the second assembly portion (122) having the surface texturing (23) on the surface (122b) of the second pair oriented on the side of the second plate (7). 4. Exchanger according to one of the preceding claims, characterized in that the second plate (7) comprises a second pair of opposite primary surfaces (7a, 7b), that (7a) of the primary surfaces (7a, 7b) oriented on the side of the intermediate element (22) having, at least in part, the surface texturing (23). 5. Exchanger according to one of the preceding claims, characterized in that at least one fin or wave leg (123) comprises a third pair of opposite secondary surfaces (123a, 123b), one and the other said surfaces (123a, 123b) of the third pair having the surface texturing (23). 6. Exchanger according to one of the preceding claims, characterized in that the fins or wave legs (123, 223) follow one another in a lateral direction (x) and extend in the passage (33) generally in a direction longitudinal (z) which is parallel to the first and second plates (6, 7) and orthogonal to the lateral direction (x). 7. Exchanger according to one of the preceding claims, characterized in that the surface texturing (23) is in the form of a porous structure having an open porosity between 15 and 60%, preferably an open porosity between 20 and 45% (% by volume), or in the form of reliefs defining, in cross section, open cavities on the surface of the first and second intermediate elements (221,222). 8. Exchanger according to one of the preceding claims, characterized in that a brazing agent (30) is arranged between the first plate (6) and the intermediate element (22) and / or between the second plate (7) and the insert (22). 9. Exchanger according to claim 8, characterized in that the brazing agent (30) is in the form of at least one coating layer arranged between the primary surface (6b) of the first plate (6) oriented on the side of the intermediate element (22) and the surface texturing (23) and / or between the primary surface (7a) of the second plate (7) oriented towards the side of the intermediate element (22) and the surface texturing ( 23). 10. Exchanger according to one of claims 8 or 9, characterized in that the brazing agent (30) has a thickness less than 300 µm, preferably between 50 and 200 µm. 11. Exchanger according to one of claims 1 to 7, characterized in that the primary surfaces (6b, 7a) of the first and second plates (6, 7) oriented towards the side of the intermediate element (22) are free of brazing agent (30) on their portions extending opposite said intermediate element (22). 12. Exchanger according to one of the preceding claims, characterized in that the intermediate element (22) is assembled in the passage (33) by assembling at least said first assembly portion (121) with the first plate ( 6), said assembly being produced by metallurgical connection of the surface texturing (23) present on that (121a) of the secondary surfaces of the first assembly portion (121) oriented on the side of the first plate (6) with the texturing surface (23) present on that (6b) of the primary surfaces of the first plate (6) oriented towards the side of the intermediate element (22), said surface textures (23) being bonded directly to each other or via a soldering (30). 13. Exchanger according to one of the preceding claims, characterized in that the passage (33) has an overall shape of parallelepiped delimited by two longitudinal edges and two lateral edges, at least one closing bar (16) extending in the height (H) of the passage (33), defined as the distance between the first plate (6) and the second plate (7) measured in a stacking direction (y) perpendicular to the plates (6, 7), along at least one of the longitudinal and lateral edges of the passage (33), the primary surfaces (6b, 7a) of the first and second plates (6, 7) oriented towards the side of the intermediate element (22) being free from texturing of surface (23) on their portions extending opposite the closure bar (16). 14. Exchanger according to claim 13, characterized in that a brazing agent (30) is arranged on the portions of the primary surfaces (6b, 7a) of the first and second plates (6, 7) oriented on the side of the element interlayer (22) extending opposite the closure bar (16). 15. Exchanger according to one of the preceding claims, characterized in that the intermediate element (22) has, before being assembled in the passage (33), a predetermined height (h), measured in a stacking direction (y) perpendicular to the first and second plates (6, 7), slightly greater than the height (H) of the passage (33), defined as the distance between the first plate (6) and the second plate (7) measured according to a stacking direction (y) perpendicular to the plates (6, 7). 16. Method for manufacturing a heat exchanger of the brazed plate and fin type, said method comprising the following steps: - arrangement of several plates (6, 7) parallel to each other so as to define a series of passages for the flow of a first fluid to be put in heat exchange relationship with at least one second fluid, - arrangement of at least one intermediate element (22) in a passage (33) formed between a first and a second plate (6, 7), - Formation of at least one contact zone or quasi-contact between at least a first assembly portion of the intermediate element (22) and the first plate (6), said first assembly portion (121) comprising a first pair of opposite secondary surfaces (121a, 121b) one of which (121a) of the surfaces of the first pair is oriented towards the side of the first plate (6) and the first plate (6) comprising a first pair of primary surfaces ( 6a, 6b) opposite, one of which (6b) is oriented towards the side of the intermediate element (22), characterized in that said secondary surface (121a) and said primary surface (6b) have at least one surface texturing ( 23) in the form of a porous structure or of reliefs formed on surfaces of the first plate (6) and of the intermediate element (22), the assembly of the first assembly portion (121) with the first plate (6) being produced without a brazing agent, said method further comprising the following steps: - application of a compressive force and supply of heat at least at the level of said contact or quasi-contact zone so as to form a metallurgical bond directly between said surface textures (23). 1/4 Figure 1 Figure 3 121a 121b 123b Figure 4 Figure 5 z 4/4 Figure 6 FRENCH REPUBLIC irai - I NATIONAL INSTITUTE PROPERTY INDUSTRIAL PRELIMINARY SEARCH REPORT based on the latest claims filed before the start of the search National registration number FA 846652 FR 1762417 EPO FORM 1503 12.99 (P04C14) DOCUMENTS CONSIDERED AS RELEVANT Relevant claim (s) Classification attributed to the invention by ΙΊΝΡΙ Category Citation of the document with indication, if necessary, of the relevant parts AT AT AT AT US 2005/121181 Al (SZULMAN CLAIRE [FR] ET AL) June 9, 2005 (2005-06-09) * the entire document * EP 3,098,554 Al (SUMITOMO PRECISION PROD CO [JP]) November 30, 2016 (2016-11-30) * the entire document * US 5,514,248 A (OKUDA NOBUYUKI [JP] ET AL) May 7, 1996 (1996-05-07) * the entire document * CN 102 322 765 A (WUXI GUANYUN HEAT EXCHANGER CO LTD) January 18, 2012 (2012-01-18) * the entire document * 1-16 1-16 1-16 1-16 F28F3 / 06 F28F13 / 18 TECHNICAL AREAS SOUGHT (IPC) F28D F28F Research Completion Date Examiner September 7, 2018 Axters, Michael CATEGORY OF DOCUMENTS CITED T: theory or principle underlying the invention E: patent document with an earlier date X: particularly relevant on its own at the filing date and which was not published until that date Y: particularly relevant in combination with a deposit or at a later date. other document of the same category D; cited in request A: technological background L: cited for other reasons O: unwritten disclosure P: interlayer document &: member of the same family, corresponding document ANNEX TO THE PRELIMINARY RESEARCH REPORT RELATING TO THE FRENCH PATENT APPLICATION NO. FR 1762417 FA 846652 This appendix indicates the members of the patent family relating to the patent documents cited in the preliminary search report referred to above. The said members are contained in the computer file of the European Patent Office on the date of) / “09“ 2018 The information provided is given for information only and does not engage the responsibility of the European Patent Office or the French Administration